A conference call is a telephone call (audio and/or video) between more than two callers or users. Thus, a user is able to speak to, and listen to, two or more other users simultaneously. A problem arises when some of the users speak softly while others have louder voices, such that some voices will be louder or softer than others. This could also be caused by differing equipment, for example if some participants in a conference call use inferior endpoint devices. In such case, listeners find themselves continually adjusting the volume of their endpoint device to normalize the volume of the respective speakers' voices.
A conference call with a plurality of participants can be conducted via multicast, or using a conference bridge or centralized server which connects numerous endpoints using appropriate unicast signaling (e.g. SIP). Mixing of the various incoming voice streams can be done at endpoint devices or at a centralized server.